Comments on: The Pipeline Disaster That Wasn’thttp://earthobservatory.nasa.gov/blogs/fromthefield/2014/02/05/alaskapipeline/?src=fromthefield-rss
NASA scientists are in the field and write home to tell about it.Wed, 30 Nov 2016 16:52:46 +0000hourly1https://wordpress.org/?v=4.5.4By: Jeff Kargelhttp://earthobservatory.nasa.gov/blogs/fromthefield/2014/02/05/alaskapipeline/comment-page-1/#comment-29649
Sat, 15 Feb 2014 00:03:42 +0000http://earthobservatory.nasa.gov/blogs/fromthefield/?p=5594#comment-29649Pete, I echo Dave’s “thank you” for clarifying and correcting the matter of the avalanche rating. Readers should defer to your guidance on that matter.
As for Yungay, in my opinion that was a very different kind of event, not clearly or simply a snow avalanche, considering how much rock debris came down. For rock avalanches, the 5-tiered rating system does not make much sense, since there can be vastly larger events, and the dynamics often are different from snow avalanches.
]]>By: Dave Wolfehttp://earthobservatory.nasa.gov/blogs/fromthefield/2014/02/05/alaskapipeline/comment-page-1/#comment-29640
Tue, 11 Feb 2014 07:10:47 +0000http://earthobservatory.nasa.gov/blogs/fromthefield/?p=5594#comment-29640Thanks for the notes, Pete!
As you may have noticed, we have now linked the reference to the railroad tunnel to a news coverage on the subject of the role it played here.
Other sources I looked into showed photos of and described a child standing in the tunnel, indicating that it was not passable by vehicle traffic as recently as the pipeline construction era, and, as you noted was never completed for rail use. There was no indication of its use, period, as it was not completed following the railroad battles of a century ago.
But the point for our write-up here was its fortuitous existence. Were it not for that tunnel, there is a strong chance the lake would have released catastrophically.
There are a few glacier-related lakes that engineers have tunneled into in order to prevent such a release elsewhere across the cryosphere.
I also suspect that the second main avalanche, that was brought down by controlled efforts, was the bigger of the two primary slides, and was also fortuitous in holding the dam together until drainages were established. Thanks for the rating details.
]]>By: Pete Carterhttp://earthobservatory.nasa.gov/blogs/fromthefield/2014/02/05/alaskapipeline/comment-page-1/#comment-29635
Sat, 08 Feb 2014 17:56:21 +0000http://earthobservatory.nasa.gov/blogs/fromthefield/?p=5594#comment-29635To this interesting analysis there are two minor corrections. The tunnel which partially drained the temporary lake was the road tunnel used prior to the road improvements for the construction of the pipeline. The railway tunnel was never completed and is an interesting story in itself.

Also, since the entire area of the mountain depicted to have avalanched was not a single avalanche but a culmination of many avalanches over many days between January 14 and 30, the size 5 rating is not accurate.

There are two rating systems for sizing avalanches. The relative area and mass system doesn’t fit a size 5 not only for the reason above, but that most of the snowpack still remains on the mountain. The majority of the debris at the valley floor came from the lower half of the mountain where the snowpack is thinner.

Applying the destructive size system, a rating of size 5 may be more accurate considering both the typical mass, 1 million tonnes, and typical path length, 3000 meters. It may have been met if it was a single avalanche. However, I submit it doesn’t really fit the description of being the largest snow avalanche known, which could destroy a village or forest area of approximately 40 hectares.

The upper end of a real destructive size 5 occurred in 1970 in Yungay, Peru.

I submit the largest of the series of avalanches off Snowslide blocking the RIchardson highway and Lowe river was artificially triggered January 25 and is a size 4.5 on the destructive scale. On the relative scale it is a size 2 based on mass and area, which shows a limitation of that scale.

We all get relative size 5 avalanches off our roofs all the time, but if Snowslide had released all of its mass over all of its area all at once, the resulting avalanche and damage would have been considerably greater. After all, not long back the pipeline company’s bridge made of one inch thick steel I-beams was lifted off its footing in a much smaller destructive size 4 event. Another steel bridge of the same design and materials was put across the runout of Snowslide Gulch as a foot bridge along the historic road, and the site of two avalanche fatalities before WW1. That bridge was demolished its first winter. Both bridges discussed are of the same stuff as the highway bridges.

Information on this event is posted in the avalanche bulletins posted by the Valdez Avalanche Center.

]]>By: Jeff Kargelhttp://earthobservatory.nasa.gov/blogs/fromthefield/2014/02/05/alaskapipeline/comment-page-1/#comment-29629
Thu, 06 Feb 2014 20:57:30 +0000http://earthobservatory.nasa.gov/blogs/fromthefield/?p=5594#comment-29629Jim, not only is Alaska’s heat your cold, but Alaska’s heat and rain is Tucson’s heat and drought. We are 60% of the way through our winter rainy season, and we (at our house) have had 0.6 inches total rainfall since Dec.1, compared to a normal about 5-6 times that. We have had serious drought for many years. Our normally resilient Sonoran Desert is having a seriously tough time coping, though on the positive and hopeful side, it evolved through climatic pressures as we are experiencing. Stay warm!
]]>By: Jim Ruebushhttp://earthobservatory.nasa.gov/blogs/fromthefield/2014/02/05/alaskapipeline/comment-page-1/#comment-29628
Thu, 06 Feb 2014 13:28:29 +0000http://earthobservatory.nasa.gov/blogs/fromthefield/?p=5594#comment-29628This is an excellent analysis. I have been following the events and record heat in Alaska. I live in the mid-west in Iowa. Your heat is our cold. We are ready for a more normal flow of the jet, too.